The present invention generally relates to systems and methods for quantifying physical motion of humans and animals. In particular, the invention relates to systems and methods employing a gyroscope attached to a subject for quantifying the subject's neurological function.
Typically, neurologists make subjective visual evaluations of patients with neuromuscular disorders. Quantifying these motions has been difficult since they frequently are random and often involve the patient's extremities, such as the hands, feet, and head, where large and heavy sensors would alter the actual motion. It has been very difficult to adequately characterize the hand tremor resulting from Parkinson's disease and to identify early non-visible tremors.
Early attempts at quantifying this type of human motion were made in France in the 19th century by Charcot. He attached a short wand at one end to the hand and on the other end he fitted a small ink pen. As the hand shook, the pen recorded the motion on a piece of paper attached to the wrist. Neither frequency information nor calibrated output was available.
More current methods have employed mechanical linkages much like dentist drill arms having a potentiometer at each linkage joint. The motion of the extremity is indicated by the potentiometers. These linkages unduly restrict the motion of the physical extremity, can create backlash, hysteresis, and limit the measurements to those capable of being taken at a fixed location.
Later approaches have employed electromyographic (EMG) surface electrodes for tremor assessment. However, remote muscle activity and electrical interference can obscure the signal indicative of the tremor. Thus, EMG equipment cannot provide low noise tremor frequency information. Furthermore, the magnitude of the rate of movement and its angular displacement can not be obtained. Finally, EMG equipment is typically cumbersome and not easily portable.
Accelerometers have also been used but have a significant limitation in that they sense not only the acceleration of a hand tremor, for example, but also that from earth's gravitational field. A slight reorientation of the sensitive axis of the accelerometer with respect to the field can cause it to record an acceleration variation without any actual tremor. The actual tremor can not be distinguished from the perceived motion with one accelerometer.
Additionally, accelerometers small enough to not influence motion of a hand do not have a low enough frequency response (i.e. wherein the low corner of the frequency response coincides with DC) and do not have enough sensitivity. Conversely, accelerometers that do have the frequency response of interest (DC to 30 Hertz) are typically too large to be used.
Accelerometers are also very impractical to use when displacement information is required because of their bias errors. Bias error is the non-zero output of the accelerometer when there is no input. The first integration of the output to obtain the velocity of the motion will generate some error due to the bias error and due to any orientation shifts as noted earlier. A second integration to obtain the displacement makes the error even larger so that displacement really has not been accurately quantified. However, the gyroscope of the present invention yields an angular rate output that needs only a single integration to obtain angular displacement. This is a critical improvement. The gyroscope bias error is very small and unlike accelerometers, the gyroscope is not sensitive to orientation in earth's gravitational field for purposes of this application.